Parkinson's disease, dementia and Alzheimer are known to degrade Brain's functionality. But are there always negative side effects to disease? Or are there any good side effect that enhances the Brain functioning?
The Savant Syndrome is the only syndrome where there is an enhancement of one particular brain function but at a heavy cost to other cognitive functions.
Savant syndrome is a condition in which someone with significant mental disabilities demonstrates certain abilities far in excess of average. The skills at which savants excel are generally related to memory. This may include rapid calculation, artistic ability, map making, or musical ability. Usually just one special skill is present.
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Miller, LK (1999). "The savant syndrome: Intellectual impairment and exceptional skill". Psychological Bulletin. 125 (1): 31–46. doi:10.1037/0033-2909.125.1.31. PMID 9990844.